1,3-Propanediol is an important chemical starting material that is potentially usable in various fields as a starting monomer for polyester and polyurethane and a starting material for synthesizing cyclic compounds.
It is known that hydration of acrolein with water in the presence of an acid catalyst yields 3-hydroxy-propanal (3-hydroxypropionaldehyde, hereinafter abbreviated as 3-HPA) and that subsequent hydrogenation of 3-HPA in the presence of a conventional hydrogenation catalyst yields 1,3-propanediol.
The specification of U.S. Pat. No. 2,434,110 discloses a process for producing 3-HPA by hydrating acrolein in the presence of an acid catalyst. In this process, an acid (e.g. sulfuric acid, phosphoric acid, oxalic acid, an acid salt or acetic acid) uniformly dissolved in an aqueous acrolein solution is used as the catalyst. In this process, sulfuric acid is preferably used and the yield of 3-hydroxypropionaldehyde is low because a condensation reaction proceeds simultaneously with the hydration. The hydration products including 3-HPA are hydrogenated in the presence of a conventional hydrogenation catalyst, if necessary, after the unreacted acrolein is removed therefrom. As the hydrogenation catalyst for converting 3-HPA to 1,3-propanediol, a catalyst containing one or more metals having hydrogenating activity, such as Ni, Fe, Co, Cu, Ag, Mo, W, V, Cr, Rh, Pd, Pt, Ir, Os, etc. is used. Since the hydrogenation reaction of 3-HPA into 1,3-propanediol proceeds very selectively, improving the selectivity of the hydration reaction of acrolein is important for obtaining 1,3-propanediol from acrolein in a high yield.
Therefore, methods for improving the selectivity of the hydration reaction of 2-alkenal, in particular, processes using a solid acid catalyst have been proposed. There have been disclosed, for example, a process using a weakly acidic cation-exchange resin catalyst (U.S. Pat. No. 3,536,763), a process using a chelate-forming ion-exchange resin catalyst (European Patent Application Laid-Open No. 0487903), a process using hydrated alumina-bound zeolite with a pore size of 5 angstrom or more as a catalyst (JP-A-5-194291 and European Patent Application Laid-Open No. 0524713), and a process using a catalyst supporting a polyacid with a first pks value of 0 to 3 (JP-A-5-221912 and European Patent Application Laid-Open No. 0544120).
However, although the selectivity of the hydration reaction of acrolein into 3-HPA has been improved in the above conventional processes as compared with the technique described in the specification of U.S. Pat. No. 2,434,110 which uses a homogeneous catalyst system, the selectivity is still insufficient and a production process having a higher selectivity is desired.
Accordingly, the object of the present invention is to provide an improved process for producing 1,3-propanediol by hydrating acrolein in the presence of a hydration catalyst to produce 3-hydroxypropanal and then subjecting the 3-hydroxypropanal to catalytic hydrogenation, which makes it possible to obtain 3-hydroxypropanal with high selectivity.